In the engine of a vehicle, an EGR valve for opening and closing an exhaust gas recirculation passage is disposed. This EGR valve consists of a valve part and a motor which is an actuator for the valve part. Typically, a valve shaft and the motor shaft of the motor are disposed separately in the EGR valve. An operation of opening the valve is performed by pressing the motor shaft against the valve shaft and moving a valve element disposed at an end of the valve shaft from a valve seat in an opening direction. Furthermore, an operation of closing the valve is performed by propagating the pushing force of a spring to the valve element via the valve shaft.
As an operation at the time of initialization of the EGR valve, the position of a motor stopper where the motor shaft is brought into contact with the stopper by retracting the motor shaft and hence the rotor becomes unable to rotate is detected first. Then, the rotor is made to rotate from the motor stopper position in the valve opening direction by extruding the motor shaft, and the position where the motor shaft comes into contact with the valve shaft is detected as a valve opening start position.
Furthermore, in the above-mentioned EGR valve, when soot (deposit) or the like included in the engine exhaust gas enters and adheres to the gap between the valve shaft and the bearing, the valve shaft cannot return to the valve closed position because of the pushing force of the spring, and may be fixed to the valve open position. This malfunction can be cleared by completely coupling the valve shaft and the motor shaft to each other in such a way that the valve shaft and the motor shaft are integrally formed with each other along an axial direction, and carrying out an opening or closing operation of forcedly opening or closing the valve shaft by using the driving force of the motor.
A conventional valve control apparatus for controlling the valve opening of a valve apparatus having a structure of not coupling a motor and a valve directly to each other is disclosed by, for example, patent reference 1. This valve control apparatus estimates the motor speed or the motor position by using the fact that a value which is obtained by integrating a motor control signal (a command duty ratio or a motor current) once is proportional to the motor speed, and the integral of this motor speed provides a value proportional to the motor position so as to correct a command opening or the motor control signal according to the estimated motor speed or motor position. By doing in this way, the conventional valve control apparatus can carry out the motor control according to the motor speed or the motor position, and can improve the motor control performance without increasing the number of sensors.